High frequency ion source formed by a discharge between a secondary-emitting electrode and a grid



- 1970 R. EVRARD HIGH FREQUENCY ION SOURCE FORMED BY A DISCHARGE BETWEEN A SECONDARY-EMITTING ELECTRODE AND A GRID Filed April 2, 1968 I N VENTOR. ROBERT EVRARD AGE United States Patent Oifice 3,532,915 Patented Oct. 6, 1970 U.S. Cl. 313-63 1 Claim ABSTRACT OF THE DISCLOSURE In a high-frequency ion source the discharge takes place between a secondary-emitting electrode and a grid be tween which a high-frequency field is set up and in which the secondary electrons return again to the electrode in one cycle.

The invention relates to an ion source, in which ions are formed in a high-frequency electric field.

In the known ion sources, the high-frequency discharge takes place in a space which has a higher pressure than the acceleration space because otherwise insufficient ions are formed. This necessitates the maintenance of a continuous gas flow from the ionization space to the acceleration space. This involves that in general only small ion extraction apertures can be used and that the efiiciency of said ion sources is comparatively low.

It is the object of the invention to provide a more favourable arrangement.

According to the invention, in an ion source in which ions are formed in a high-frequency electric discharge, said electric discharge occurs between two electrodes one of which is secondary-emitting and invention, a pressure lower than, for example, 10 Torr is no objection for maintaining the electron production and therewith the ionisation of the gas.

In order that the invention may be readily carried into effect, it will now be described in greater detail, by way of example, with reference to the accompanying drawing, which digrammatically shows a cross-sectional view of an electrode arrangement for an ion source according to the invention.

Referring now to the figure, reference numeral 1 denotes a hollow electrode, radius 12 cm., the surface of which consists of oxidized silver. 2 is a copper grid having wide meshes and arranged concentrically with l, radius 9 cm. An extra electrode 3 is arranged in the centre of 1 and 2 and is supported by a quartz plate 4. An accelerating electrode is denoted by 5. In the space between the electrodes a deuterium-tritium mixture is provided at a pressure of IO- torr. An alternating voltage from source 6 of approximately 40 mc./s. and v. amplitude is set up between the electrodes 1 and 2. Electrode 1 is 500 volts negative with respect to 2. 5 may be a few tens of kv. negative with respect to 3. Ions formed in the space between 1 and 2 are introduced into the accelerating space of electrode 5, through electrode 3, The arrangement is suitable for a neutron generator.

What is claimed is:

1. An ion source comprising two spaced electrodes defining a region filled with a gas forming ions during an electrical discharge; one of said electrodes being secondary-emitting and the other grid-like, and means to produce a high-frequency electric field between said electrodes having an amplitude and frequency such that emitted secondary electrons return again to the secondaryemitting electrode after one cycle.

References Cited UNITED STATES PATENTS 10/1960 Heil ct al. 313-63 10/1951 Hernquist 2504l.9

US. Cl. X.R. 3 l3103 

